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It's virtual money, based on a pyramid scheme. As long as more people buy into it, the value keeps going up.
It's not that different from gold. (although that still has some practical uses). The value of gold depends on what people want to pay for it, while it takes more and more energy to mine more gold. Instead of having the extract harder and harder to reach gold, bitcoin is based on a algorithm that gets harder and harder to find the next value. Compare it to finding all prime numbers to infinity. First ones are easy and it gets harder as you keep going.
Gold is much more environmentally friendly to mine though: The carbon footprint of a single mined bitcoin (including fees) amounts to 191 tonnes of carbon dioxide while to mine the equivalent value in gold, it would only take 13 tonnes of carbon dioxide.
Transactions in Bitcoin are part of a decentralized ledger that can't be manipulated since everyone has the ledger. You would have to change every single instance of the ledger simultaneously to perform a Bitcoin heist in such a way that everything still adds up from the start. Impossible. (so far) Transactions in bitcoin also cost a lot of energy, updating the ledger takes a lot of mathematics. 1 bitcoin transaction has the equivalent carbon footprint of 126 thousand hours of watching Youtube or 1.6 million visa transactions.
https://www.visualcapitalist.com/comparing-the-carbon-footprint-of-gold-and-bitcoin/
It's also all shrouded in anonymity. You have a key to access your bitcoin wallet. Hence it's popular in the black market and dark web. No records for tax agencies to look through, no way to trace transactions and as long as people support it and buy into it, a perfectly safe way to hide your money. So far the distrust in governments apparently outweighs the negative impact of bitcoin currencies on the environment and people keep supporting them.
If you value the future of your children, stay away from bitcoin and equivalent currencies.
